Stainless Steel Rebar Re-bending at the same location 2

[rajeshkumarn]

Will the stainless steel rebars used for bridge deck weaken when it is bent at a location? The second part of the question is what will happen if the bent stainless steel rebar bent again at the same location? I have a situation where the contractor wants to bend the SS rebar 90 degrees in a stage construction of the bridge due to limited space between the existing portion of existing structure and want to bend it back to a straight line in the next stage when the existing structure is demolished, so that he can use this portion of rebar for lapping in a closure pour. Any answers will be appreciated.

 

[bridgebuster]

Here's a study that was done over 20 years ago that addresses field bending/straigntening bars. obviously it doesn't discuss SS bars. It recommends heat bending but I've never seen anyone do it.

 

[rajeshkumarn]

Thanks bridgebuster. All the reports and references I have also talk about bending, but none of them talk about straightening back at the same location that was bent. There was no references online too.

 

[TXStructural]

Do not hot bend stainless. It will change the metallurgy and result in premature corrosion.
Field bending should be avoided, and the preferred method would be couplers. That said, #3, #4, and #5 can be field bent if absolutely necessary. As with all rebar, they may be bent and straightened in the same length one time only. Stainless bar does have a very high ductility as rebar goes, but the high yield strength also means it is very difficult to bend by hand or using hand tools. Do not use carbon steel tools to bend of straighten stainless, as doing so embeds small particles of carbon, resulting in focal points for corrosion. It may also be necessary for the surface to be passivated with pickling paste after bending/straightening, depending on the type of stainless.

Do not allow both the bending and straightening to be done in the field by hand. Field bending typically results in too-tight of bend radius and this is the mechanism where the bar is weakened or fractured outright. Place shop-fabricated bar, then straighten as the staging permits, avoiding kinks and tight radius re-bends. The loss of strength should be nil to minimal.

CRSI has a free tech note on stainless reinforcement on the website at crsi.org

 

[bridgebuster]

TX - thanks for the info. I'm also working on a redecking project with about 3 million lbs of stainless - No. 4 to 6. We don't anticipate any bending/restraightening, but then again...

Our staging doesn't allow for closure pours,not enough room, all transverse bars will be coupled.

I wasn't aware of the restriction on carbon tools. We anticipate quite a bit of field fabrication due to the construction staging and bridge geometry.

Thanks again.

 

[TXStructural]

BB, If you don't mind me asking, what part of the world is that project being undertaken? I was just on a phone conference where we were talking about stainless bridge decks, and that didn't come up. (You can contact me offline...)

John Turner CSP PE
CRSI Greater Southwestern Regional Manager

 

[bridgebuster]

John - I sent you an e-mail.

 

[rajeshkumarn]

thanks John and bridgebuster. We ended up recommending the contractor to use couplers. The client had a concern that during the making of the couplers there could be some other metal deposited in them which in turn could react with stainless steel.